Terahertz time-domain spectroscopy as a novel tool for crystallographic analysis in cellulose
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ORIGINAL RESEARCH
Terahertz time-domain spectroscopy as a novel tool for crystallographic analysis in cellulose Han Wang . Yoshiki Horikawa . Satoru Tsuchikawa . Tetsuya Inagaki
Received: 2 April 2020 / Accepted: 1 October 2020 Ó Springer Nature B.V. 2020
Abstract Terahertz (THz) radiation is responsive to optical phonons in crystal lattices; therefore, THz time-domain spectroscopy (THz-TDS) has potential utility in crystallographic analysis. In this study, THzTDS was used to investigate cellulose samples extracted from different sources with varying ratios of Ia and Ib fractions. This is the first study to report that the absorption coefficient in the THz region of cellulose Ia and Ib presents different characteristic absorption peaks around 2 THz. This can be used to distinguish the cellulose I allomorph, which exhibits differences in its crystalline structure. The absorption coefficient at 2.11 and 2.38 THz showed a considerable linear correlation with the Ia fraction of the cellulose samples. The absorption coefficient spectra of 1.88–3.40 THz were further detrended and separated into three Gaussian peaks. The correlations between the parameters of these separated peaks (integrated intensities, peak positions) and the Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03508-9) contains supplementary material, which is available to authorized users. H. Wang S. Tsuchikawa T. Inagaki (&) Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan e-mail: [email protected] Y. Horikawa Institute of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
crystalline structural values (d-spacing, crystalline size, crystallinity index) that calculated from the X-ray diffraction (XRD) pattern were investigated. Keywords THz-TDS Cellulose Crystalline allomorph Crystallinity Cellulose Ia Cellulose Ib
Introduction Cellulose is the most abundant and widely distributed polysaccharide in nature. It is an important component of the structural framework of plant cell walls and is synthesized by cellulose synthetases on cytoplasmic membranes. Cellulose has a linear chain composed of b (1 ? 4)-D-glucose units that contain hydrogen bonds arranged in a parallel fashion (Updegraff 1969), where cellulose I is the crystalline cellulose that is naturally produced by plants, algae, and bacteria. Cellulose I has been found to consist of two polymorphs: Ia has a triclinic structure and contains one cellulose chain, and Ib has a monoclinic structure and contains two cellulose chains (Sugiyama et al. 1991). The two polymorphs coexist according to the different proportions of cellulose sources (O’sullvian 1997; Azizi Samir et al. 2005; Nishiyama 2009). For instance, the cellulose found in bacteria and algae such as Cladophora spp. and Valonia ventricosa is composed mainly of the Ia type, whereas the cellulose of the secondary cell walls of higher
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